Method of consolidating earth formations without removing tubing from well



Jan. 13, 1970 s, MILLHONE ETAL 3,489,222

F CONSOLIVDATING EARTH FORMATIONS OUT REMOVING TUBING FROM METHODQO WELL WITH

Filed Dec. 26, 1968 '3! II INVENTORS United States Patent 3,489,222 METHOD OF CONSOLIDATING EARTH FORMA- TIONS WITHOUT REMOVING TUBING FROM WELL Ralph S. Millhone, Brea, Chester L. Love, La Habra, Alexander S. Allen, Jr., Santa Monica, and Coral L. DePriester, Moraga, Califl, assignors to Chevron Research Company, San Francisco, Calif., a corporation of Delaware Continuation-in-part of application Ser. No. 730,513, May 20, 1968. This application Dec. 26, 1968, Ser. No. 787,150

Int. Cl. E21b 33/138 US. Cl. 166-290 5 Claims ABSTRACT OF THE DISCLOSURE A method of consolidating an unconsolidated formation penetrated by a cased well having a production tube located therein without removing said tube from the well by positioning a flushing tube inside the production tube, removing unwanted sand from the bottom of the well, placing an injection leveling material in the formation, injecting sand consolidation fluids down the flushing tube and into the formation to consolidate the formation and removing the flushing tube from the production tube to place the well in a condition for further use.

This application is a continuation-in-part of copending application Ser. No. 730,513, filed May 20, 1968.

This invention relates to a method of removing sand from a cased well having a production tubing located therein and preventing further sanding of the well without removing the production tube by means of inserting a flushing tube into the production tube and circulating out sand from the well, then packing off the flushing tube and injecting a series of sand consolidating fluids including a permeability leveling fluid through the flushing tube down the well and into the formation to consolidate the formation.

A serious problem is often caused during production of oil from wells by sand entering the well with the production fluids and accumulating to a point where production from the well is hindered or even halted because of the sand in the well. In many wells sand entering the well with the production fluids is also undesirable because of the damage that the sand can cause to the tubing and surface equipment by abrasion. Many techniques of sand consolidation have heretofore been practiced to control the flow of sand into wells. For example, methods of sand consolidation are described in US. Patents 3,176,767, 3,176,768 and 3,176,769. Generally, these sand consolidation techniques are accomplished by injecting a resin into the formation and by consolidating the resin to hold the sand grains in place. These techniques require careful placement of the resin to insure adequate coverage over the entire treated interval. This usually limits the techniques to thin zones or requires that the consolidation fluids be injected into the formation by special tools. These special tools have a diameter approaching the diameter of the casing in which they are used. The production tubing must be removed from the hole while removing sand and running these special tools since, as noted, the diameter of the tools approaches the diameter of the casing. There is need, therefore, for a method of removing sand from a well and preventing further sanding of the well in which a casing and a production tubing are located without removing the production tubing from the well. This is particularly true in deep offshore wells 3,489,222 Patented Jan. 13, 1970 where pulling the tubing constitutes a major operation.

As noted in our present application Ser. No. 730,513, filed May 20, 1968, there is a serious problem in consolidating unconsolidated formations penetrated by a well because of the nonuniform permeability distribution that almost always occurs in such formations. This problem is particularly troublesome where, for space or other reasons, injection tools cannot be used since these tools are necessarily near full bore size to permit casing packoff. There is need, therefore, for a method of removing sand from a well and then consolidating the formation producing the sand without need of removing tubing from the Well and in such a manner to insure that the distribution of sand consolidation fluids in such formation is relatively even.

Briefly, the present invention provides for consolidating a formation penetrated by a cased well having a production tube located therein without removing the production tube from the well and completing such consolidation in such a manner to provide for relatively uniform placement of the consolidation fluids in the well to insure a successful operation. In accordance with the invention, a flushing tube of smaller diameter than the production tube is inserted into the production tube and down the well. The outer diameter of the flushing tube is such that an annulus is formed between the production tube and the flushing tube. The flushing tube is lowered to approximately the sand level in the well and a fluid is circulated to remove sand from the well. Circulation may occur down the flushing tube and up the annulus between the flushing tube and the production tube. Alternatively circulation may be down the annulus and up the flushing tube. After the sand in the well has been removed by such circulation the annulus between the production tube and the flushing tube is packed off. This pack off is usually accomplished by closing in the annulus at the surface. Usually it is then necessary to inject a slurry of specially selected sand in a fluid down the flushing tube and out into the formation to replace the formation sand previously produced. After the injected sand has been located in the formation, a permeability leveling material is injected down the flushing tube and out into the formation to provide for more uniform placement of the later injected sand consolidation fluids. The permeability leveling material is carried in a liquid carrier to facilitate its injection through the flushing tube. After such permeability leveling material is in place in the formation, sand consolidation fluids are then injected down the flushing tube and into the formation to consolidate the sand in the formation to prevent further sanding of the well.

More specifically, the invention provides for injecting down the flushing tube and into the formation a permeability leveling mixture comprising a mixture of parts by volume of a hydrocarbon oil, from 15 to 35 parts by volume of a selected low molecular weight alkanol and from 0.005 to 0.25 part by weight of a permeability leveling compound per 100 parts by weight of the above mixed liquids. After such permeability leveling material is located in the formation sand consolidation fluids are sequentially passed down the flushing tube and into the formation. Such sand consolidation fluid sequentially includes a liquid resinous material curable to an infusible solid state by treating with a curing agent; a liquid hydrocarbon and a curing agent to convert the liquid resinous mixture to the infusible solid state to consolidate the sand in the formation adjacent the well.

It is a particular object of the present invention to provide a method of sand consolidation for use in consolidating sand in a well having a casing and a production tubing located therein without removing the production tubing from the well. Further objects and advantages of he present invention will become apparent from the folowing detailed description read in light of the accompanying drawings which is made a part of this specifica- :ion and in which:

FIGURE 1 is a sectional view of a cased well having 1 production tube located therein, said well penetrating 1 producing formation which has sanded up the well;

FIGURE 2 is a sectional view and shows a flushing :ube located in said well for use in circulating undesirable ;and from the well;

FIGURE 3 is a sectional view and shows a flushing :ube located in said well for use in sand packing of the :leanout well;

FIGURE 4 is a sectional view and shows a flushing tube located in a well for use in injecting sand consolidation fluids into the sand packed well; and

FIGURE 5 is a sectional view and shows said well ready to return to production.

Referring now to FIGURE 1, a Well 20 is shown penetrating various nonproductive earth strata 22 and 24 and a producing strata or zone 26. The well is cased over the nonproduetive intervals 22 and 24 by means of suitable casing 28. A production liner 30 having slots 32 is used to line the well adjacent the oil producing zone 26. Alternatively, the well may be cased over its entire depth and the producing intervals perforated. Production tubing 34 extends down the Well to the vicinity of producing zone 26 for production of fluids therefrom. The annulus 36 between the well casing 28 and the production tubing 34 is packed off by suitable means such as a production packer 38. Thus well fluids are produced up production tubing 34. As known in the art, production may be by natural flow or production may be assisted by artificial means such as by pumping or gas lift. As illustrated schematically in FIGURE 1, sand particles 40 from formation 26 have entered the well through the slots 32 in liner 30 and have plugged the well to a point where production from the well is hindered or, in some cases, halted.

In accordance with the invention and as illustrated in FIGURE 2, a flushing tube 42 of smaller diameter than the diameter of the production tubing 34 is run down the inside of the production tube 34 forming an annulus between the inside of the production tube 34 and the outside of the flushing tube 42. This annulus should preferably have at least as great a cross sectional area as the cross sectional flow area inside the flushing tube. Usually the flow area of the annulus is somewhat greater than the flow area of the flushing tube. It is desirable to extend the flushing tube 42 down the production tube 34 and into the upper portion of the sand located in the lower portion of the well. Fluid is then circulated to remove sand from the Well. Fluid may be circulated down the flushing tube 42 and up the annulus between production tube 34 and flushing tube 42 or alternately down the annulus and up the flow tube. The latter circulation arrangement is desired because it prevents possible bridging of sand in the annulus around the flushing tube in the production tube which could cause possible sticking of the flushing tube. A pump 44 is used to circulate the fluid used to remove undesirable sand from the Well. The circulating fluid may be, for example, water, oil or foam. The circulation of such fluid will often remove undesirable loose sand located immediately adjacent the outside of the casing as is illustrated by the void 48 adjacent liner 30.

After the undesirable sand has been removed from the well, it is sometimes desirable to pack the space exterior of the liner with new sand before injecting sand consolidation fluids. This is particularly true in cases Where the liner has failed. Such liner failure commonly requires sand consolidation to permit further production from the zone. Prior to injecting such new sand down the flushing tube 42 the annulus 46 between the flushing tube 42 and the production tubing 34 is packed off by suitable means such as packing means 50. Closing this annulus promotes entry of fluids injected down the flushing tube 42 into the producing formation 26 through slots 32 in production liner 30. A liquid slurry of sand, generally coarser than the formation sand, is now injected through pump 44 and down the flushing tube 42 and into formation 26 through the slots 32 in liner 30 to fill the void 48 adjacent the liner. The coarse sand is selected so that it will pass through the liner. After a predeterminable amount of coarse sand has been injected to fill the void behind the liner 30, injection of such slurry containing the sand is stopped. The formation is now ready for the sand consolidation operation.

As shown in FIGURE 4 the well is ready to first receive the permeability leveling material. In accordance with the preferred form of the present invention the permeability leveling material comprises a mixture of hydrocarbon oil, a permeability leveling additive preferably a cellulosic material and a polar organic compound capable of swelling the cellulosic material. This permeability leveling material is injected into a formation prior to the injection therein of a liquid resin useful to consolidate the formation. The permeability leveling material containing the cellulosic material and the polar organic compound acts to balance fluid injectivity into the formation and to remove any water which may be in the formation in the vicinity of the well. Water removal is an important step in the consolidation process and must be done to insure adequate strength in the consolidated sand.

The cellulosic materials which may be employed in the practice of the invention are the lower alkyl cellulose ethers, e.g. methylcellulose, ethylcellulose, propylcellulose, butylcellulose and benzylcellulose. Ethylcellulose is the highly preferred cellulose ether for use in the practice of the invention. Ethylcellulose is obtainable on the market under various trade names such as Ethocel. Ethylcellulose is an ether of cellulose formed by reaction of chloroethane with cellulose which has been reacted with a strong base. The ethylation of cellulose has been long known in the art. Preparation of ethylcellulose is possible by a variety of well known methods. Ethylcellulose is described and methods of making ethylcellulose are disclosed in an article in Colloid Chemistry J. Alexander, vol. V1, p. 934, Reinhold, 1946.

Ethylcellulose is available as particulate material. A preferred form of ethylcellulose has a dry particle distribution such that about of the particles by weight pass a 35-mesh screen and 10% by weight pass a 400- mesh screen. The median particle size is approximately -mesh. When mixed with a carrier fluid such as diesel oil containing a selected low molecular Weight alkanol ethylcellulose will swell to a volume far exceeding its dry volume. Wet volume to dry volume ratios of between about 3 to 6 are suitable in accordance with the invention. A ratio of about 5.5 is considered optimum. While the swell ratio depends somewhat on time and concentration of alkanol in the carrier fluid, a ratio within the above range will give good results.

Cellulose ethers used in the present invention may have a molecular weight of any value which permits pouring and mixing a composition of the invention without undue thickening. The cellulose is mixed with a hydrocarbon oil and a sufllcient amount of a polar organic compound capable of swelling the cellulose at a desirable rate. The polar organic material is preferably a low molecular Weight alkanolfor example, methanol, ethanol, propanol, butanol, pentanol and hexanol. The preferred polar organic compound for this use is Z-propanol. Controlled swelling of the ethylcellulose was obtained by slurring dry ethylcellulose with a mixture of 2-propanol and diesel. Fifteen minutes or more contact with between 15-30% by volume 2-propanol in diesel causes swelling of the ethylcellulose to four to five times its original volume. The swelling properties do not change significantly with added time. The mixture is useful as a diverting agent when ethylcellulose is slurried in a mixture of between 15 and 30% by volume 2-propanol and diesel oil. Higher 2-propanol concentrations, i.e., greater than 35%, tend to dissolve the ethylcellulose, while lower Z-propanol concentrations, i.e., less than 15%, give insufficient swelling for adequate diverting in accordance with the present invention.

After such permeability leveling fluid has been injected into the formation the remainder of the sand consolidation fluids are injected down flushing tube 42 and through the slots 32 in liner 30 and into formation 26 to consolidate the sand around the well. The sand consolidation fluids are injected sequentially down the tube 42 and out into the formation so as to provide a permeable consolidation region around the well. In a preferred embodiment the sand consolidation fluid sequence includes a liquid resinous mixture curable to an infusible solid by treating with a curing agent; a liquid hydrocarbon; and a curing agent to convert the liquid resinous mixture to a solid state to bond the sand grains together.

In accordance with the invention a permeability leveling material is injected into unconsolidated strata prior to the injection of sand consolidation fluids to provide for leveling the permeability of the strata so that the later injected sand consolidation resin will tend to be more uniformly distributed in the strata. The permeability leveling material is carried in a liquid carrier which also acts as a water scavenger to remove water from the formation to better prepare it for the resin which follows. Thus the permeability leveling fluid which is injected is a mixture of a hydrocarbon oil, a selected polar organic compound preferably a low molecular weight alkanol and a fluid leveling additive. A mixture of the above type is injected into the unconsolidated interval prior to the injection of resin therein. The low molecular weight alkanol acts as a water scavenger and in addition assists in promoting the action of the permeability leveling additive.

The preferred form of the invention provides for injecting into the formation prior to the injection of the consolidation resin a mixture of 100 parts by volume of a hydrocarbon oil, from 15 to 35 parts by volume of a selected low molecular weight alkanol and 0.005 to 0.25 part by weight of a permeability leveling cellulosic compound per 100 parts by weight of the above mixed liquids. The above noted mixture is an effective diverting agent useful to promote relatively uniform placement of sand consolidation liquids in a formation composed of strata having different permeability. In addition, the mixture is an effective water scavenger useful to remove water from the formation prior to the resin injection step of a sand consolidation operation. The injection of this mixture is followed by the injection of a sand consolidation resin and a suitable curing agent for the resin to provide a permeable consolidated formation in the vicinity of the Well.

A field test was conducted in accordance with the present invention. A one-inch tubing was run through a 2%" production tubing to the 11 of production perforations between 7311 and 7336 depths in a well. The production interval was sand packed with 50 cubic feet of fine sand prior to preparing for consolidation. The permeability leveling material injected in this field test comprised 007 pound of ethylcellulose diverting agent per barrel of an 80-20 mixture of diesel oil and 2-propanol. This material was injected to prepare the fluid injectivity profile of the formation for consolidation.-Consolidation fluids were then injected into the formation. The one-inch tubing was periodically reciprocated through the production interval during placement of preparation and consolidation fluids. Injection data are shown in Table I.

TABLE I Injection Cumulative Rate Surface Time, Cumulative Volume, Barrels/ Pressure, Mlnutes Barrels Minute p.s.i.

0 0 Permeability Leveling 0 1, 500

Material. 10 10 Permeability Leveling 1 1,500

Material. 31 30 Permeability Leveling 1 1, 600

M eri 41 40 Permeability Leveling l l, 420

Materi 110 Permeability Leveling 1 l, 500

Material. 138.-- l0 Resin 75 1,300 5 Permeability Flush 1 1,300 20 Permeability Flush 25 l, 150- 202 22 Permeability Flush l 150 234 2s Activator 1 200 The field test is believed to have been successful in uniformly consolidating the formation through a one-inch tubing.

Although only specific embodiments of this invention have been described in detail, the invention is not to be limited to only such described embodiments but rather the invention is meant to encompass all equivalents coming within the scope of the appended claims.

We claim:

1. A method of removing sand from a well and preventing further sanding of the well, said well having a casing and a production tubing located therein, without removing the production tube from the well comprising the steps of packing off the annulus between a casing and a production tube located in a well, positioning a flushing tube inside said production tube to form an annular passage between said flushing tube and said production tube, circulating a fluid in the flushing tube and the annulus between said flushing tube and said production tube to remove sand from said well, closing off the annulus between said production tube and said flushing tube, injecting a permeability leveling material down said flushing tube and into said formation to assist in leveling the injection profile of said formation, injecting sand consolidation fluids down said flushing tube and into the formation to consolidate sand in the formation, removing the flushing tube from the production tube and producing the Well through the production tube.

2. The method of claim 1 further characterized by passing a slurry of coarse sand in a fluid down said flushing tube and into the formation prior to injecting said sand consolidation fluids into said formation.

3. The method of claim 1 further characterized in that the sand consolidation fluids are sequentially passed down the flushing tube and include a liquid resinous material curable to an infusible solid state by treating with a curing agent; a liquid hydrocarbon and a curing agent to convert the liquid resinous mixture to the infusible solid state.

4. The method of claim 1 where the permeability leveling material comprises a mixture of 100 parts by volume of hydrocarbon oil, from 15 to 35 parts by volume of a selected low molecular weight alkanol and from 0.005 to 0.25 part by weight of a cellulosic material per 100 parts by weight of the above mixed liquids.

5. The method of removing sand from and preventing sanding of a well having a cased borehole having a production tube within and approximately concentric with the casing which comprises packing the annulus between the casing and the production tube, positioning a flushing tube of smaller diameter than the production tube within the production tube, the flushing tube extending to the sand at the bottom of the well, circulating a fluid in the flushing tube and the annulus between the flushing tube and the production tube to remove sand from the bottom of the borehole, closing off the annulus between the production tube and the flushing tube, passing a slurry of selected sand in an aqueous fluid down the flushing tube and into the formation, passing down the flushing tube and into the formation in sequence first a permeability leveling 7 material; second a liquid resinous mixture curable to an 2,852,078 infusible solid by treatment with a curing agent; third 8. 3,123,138 liquid hydrocarbon; and fourth a curing agent to convert 3,134,436 the liquid resinous mixture to a solid, removing the fiush- 3,302,715 ing tubing and then producing the Well. 5

References Cited STEPHEN UNITED STATES PATENTS 2,573,690 11/1951 Cardwell et al. 166-295 2,761,511 9/1956 Billue 166292 10 Krause 166285 X Robichaux 166295 Means et al. 166295 X Smith et a1 166--292 X NOVOSAD, Primary Examiner US. Cl. X.R. 

